The present invention relates to electric power switches, and more particularly to an electric power switch, such as an electromagnetic contactor or circuit breaker, having an improved performance.
A conventional electric power switch such as an electromagnetic contactor is designed as shown in FIG. 1. In FIG. 1, reference numeral 1 designates a plastic mounting base; 2, a stationary iron core formed by stacking silicon steel plates; 3, a movable iron core which is a laminate of silicon steel plates; 4, an operating coil for providing a drive force which causes the stationary iron core 2 to attract the movable iron core 3 against the elastic force of a tripping spring (not shown); and 5, a cross bar made of plastic, the cross bar 5 having a rectangular window 5A and holding the movable iron core 3 at the lower end. Further in FIG. 1, reference numeral 6 designates a movable contact piece inserted into the rectangular window 5A of the cross bar 5; 6A, a movable contact on one end of the movable contact piece 6; 7, a spring adapted to depress the movable contact piece 6; and 8, a stationary contact piece having a stationary contact 8A on one end and a terminal 8B at the other end and arranged in such a manner that it is engageable with the movable contact 6A. When the contacts 6A and 8A are in contact with each other, current flows from the stationary contact piece 8 to the movable contact 6. Further in FIG. 1, reference numeral 9 designates a terminal screw for connecting the electromagnetic contactor body to an external circuit; 10, a base on which the stationary contact piece 8 is mounted; 11, an arc cover which covers the electromagnetic contact; 12, an arc formed between the stationary contact 8A and the movable contact 6A; and 13, metal arc-extinguishing plates made of a magnetic material and used for extinguishing the arc 12, the plates 13 being arranged parallel to the joint surface of the stationary contact piece 8 and the stationary contact 8A. The abovedescribed components are arranged symmetrically with respect to the central axis of the electromagnetic contactor. FIG. 1 shows a sectional view of the right-handed half of the contactor.
When the operating coil 4 is deenergized, as shown in FIG. 1, the movable iron core 3 is disengaged from the stationary iron core 2 by the tripping spring (not shown). Accordingly, the movable contact 6A and the stationary contact 8A are moved apart from one another, as a result of which an arc 12 is created between the contacts 6A and 8A. The arc 12 thus created, being attracted by the magnetic metal arc-extinguishing plates 13, moves from the state designated by 12B to that designated 12A. Finally, the arc is extinguished between the metal arc-extinguishing plates 13, and thus the current is interrupted.
In the conventional power switch constituted as described above, of the plurality of metal arc-extinguishing plates, only those which are located between the movable contact piece 6 and the stationary contact piece 8 contribute to arc extinction. Accordingly, the conventional power switch suffers from drawbacks that its interrupting performance is low and its contacts are rapidly consumed.
An electric power switch as disclosed by U.S. Pat. No. 4,429,198 has recently been proposed to overcome these difficulties. That electric power switch, as shown in FIG. 3, includes a plurality of metal arc-extinguishing plates 13 arranged perpendicular to the joint surface of the stationary contact piece 8 and the stationary contact 8A, and a commutation electrode 15 located between the movable contact piece 6 and the stationary contact piece 8 when the latter are disconnected from each other. However, that electric power switch is disadvantageous in that, since the metal arc-extinguishing plates 13 are remote from the arc 12, it cannot sufficiently drive the arc, and accordingly the arcing period is relatively long. Accordingly, especially in the case where it is required to interrupt a small current, because of the insufficient arc driving capacity described above, the arcing period becomes long when the voltage is high. Thus, the current interrupting performance is still unsatisfactory.